1. Field of the Invention
The invention relates to a machine for producing a fibrous material web, in particular a paper or cardboard web.
2. Discussion of Background Information
The web is mechanically stressed in the pickup of the paper web in the press section by rolls, felts and transfer belts, and in pickup in the drying section by the first cylinders. This stress leads to a stretching of the paper web, and a break can even occur if the strain is too great. The level of the maximum permissible stress depends on the dry matter content of the web. It is known that web strength increases with an increasing dry matter content. If the paper machine speed increases, the resulting stress on the web in the pickup by rolls, felts, transfer belts, cylinders, etc., also increases. In the design of fast-running paper machines it is therefore particularly important for the dry matter contents of the web to conform to the prevailing conditions at the points of high stress. For this essential reason, machines for speeds above about 1600 m/min are virtually all equipped with so-called tandem presses. This press concept has a shoe press at least in the second press in order to obtain the necessary dry matter content in the pickup from the first cylinder.
Apart from the necessary dry matter content, a reliable web travel is also important for fast-running paper machines. This means that great importance is attached to measures for avoiding a web edge flutter, as fluttering web edges tend to lead to tearing or crease formation, particularly at high speeds.
The corresponding machine concepts hitherto known have the disadvantage that the dry matter contents which are achieved before the first free draw are too low, and a trouble-free web travel cannot be ensured. This means that, depending on the wet strength of the stock used, an economical production is not possible at speeds of over about 1700 m/min.